Transmissible spongiform encephalopathies (TSE), also known as prion diseases, are a group of neurodegenerative diseases that affect humans and animals. Creutzfeldt-Jakob disease (CJD), kuru, Gerstmann-Straussler-Scheiker diseases (GSS), and fatal familial insomnia (FFI) in humans, as well as scrapie and bovine spongiform encephalopathy (BSE) in animals, are examples of TSE diseases.
It is known that a key characteristic and marker of prion diseases is the formation of an abnormally shaped protein named PrPSc. However, prion diseases are characterized by an extremely long incubation period. Thus, concentrations of PrPSc are at low levels for a long period of time. As such, one important objective of prion research has been to detect small amounts of PrPSc in diverse samples.
PrPSc is a post-translationally modified version of a normal protein, termed PrPC. PrPC is found naturally on the membranes of animal and human cells. The infective unit of PrPSc is understood to be a β-sheet rich oligomeric structure, which converts PrPC to PrPSc by integrating PrPC into a growing aggregate (FIG. 1). In light of this replication model, it has been found that PrPSc can be detected with high sensitivity by protein misfolding cyclic amplification (PMCA). See U.S. Pat. No. 7,351,526 and U.S. Patent Application Pub. No. 2006/0263767, each of which is incorporated by reference herein it its entirety. In the context of prion diseases, PMCA-based PrPSc detection typically involves: (i) contacting a sample with PrPC (e.g., by contacting a suspected diseased sample with a tissue homogenate containing PrPC); (ia) incubating the sample/PrPC mixture; (ii) disagreggating any aggregates formed during step (ia) (e.g., by sonication); (iii) repeating steps (ia) and (ii) a plurality of times; and (iv) detecting the presence of PrPSc within the sample (e.g., by western blotting). See FIG. 2.
What is still needed in the art, however, is a quantitative procedure for determining the concentration—rather than merely detecting the presence—of PrPSc in fluids and tissues. The present embodiments disclose such a procedure.